Watch: Cristiano Ronaldo 'is a player who can cause a great mess to rivals' - Zidane

Real Madrid manager Zinedine Zidane insists Cristiano Ronaldo should never be doubted as the Portuguese forward continues to rediscover his goalscoring form.

Ronaldo, 31, has scored 18 goals in his past 18 appearances in all competitions, including two goals in the 3-1 win over Paris Saint-Germain in the first leg of the Uefa Champions League last-16 tie on Wednesday.

While Ronaldo's 11 goals in 18 Primera Liga matches is a decent return, it falls short of his usual standards set in previous seasons, and has contributed to Madrid's domestic struggles that has seen the club fall 17 points behind rivals Barcelona in the Primera Liga table. Madrid are in fourth place, 10 points behind Atletico Madrid in second, albeit having played one game less.

However, Ronaldo's form in the Champions League has been remarkable, with 11 goals scored in seven games to etch his name in the history books.

After the success against PSG in midweek, Ronaldo and Real Madrid turn their attention back to league duties on Sunday when they travel to face ninth-placed Real Betis, and Zidane has warned against writing off the threat posed by Ronaldo.

"Cristiano is one of those players you can´t doubt about, even when he´s not scoring," Zidane said during his pre-match press conference on Saturday. "He´s a player who can cause a great mess to the rival with very few chances to score and we all know this.

"I don´t know if he´s in his best shape now, but he knows there´s a long season ahead of us, we all know that, and he´ll be there. But we're all talking about the PSG second leg and there are five league matches before that. For me it is important what we are going to do before that."